As technology has advanced in the areas of cellular communications and networks, low power devices, and multimedia standards, a range of new applications have been developed. As these technologies continue to mature, the applications from these different areas will come together, and what will eventually emerge is a portable multimedia terminal. This is a low-power, portable device that is capable of both transmitting and receiving voice, video, and data through the wireless network. Multimedia data requires a large amount of bandwidth, so these multimedia terminals will need to use the next generation cellular systems which can provide the necessary bandwidth to each terminal. These terminals will also need to be light-weight for portability, which requires a minimization of battery size and hence the use of state-of-the-art low power design techniques. Finally, it is important that these terminals use standardized compression and communication methods in order to facilitate interoperability among different devices. These multimedia terminals will open up many new applications, such as video cellular phones and wireless web browsing. However, there are problems that need to be addressed before transmission of multimedia data over wireless networks can become commonplace.
Mobile multimedia terminals must be able to transmit video over the low-bandwidth, error-prone wireless networks such that the decoder obtains high quality reconstructed video. Video data has a very high data rate and thus needs to be compressed before it can be transmitted across the bandwidth-constrained wireless channel. Video is typically compressed using international standard compression methods, such as the MPEG or H.263 standards. These standard video compression methods use predictive coding (motion compensation) of the frames and variable length codewords to obtain a large amount of compression. This makes the compressed video bitstream sensitive to channel errors, as predictive coding causes errors in the reconstructed video to propagate in time to future frames of video, and the variable-length codewords cause the decoder to easily lose synchronization with the encoder in the presence of bit errors. Once synchronization is lost, the decoder may not be able to correctly decode the remainder of the bitstream, even if no further bits are in error.
The MPEG4 video compression standard incorporated several error resilience tools into the standard to make the compressed bitstream more robust to channel errors. These tools include resynchronization markers, header extension codes, data partitioning, and reversible variable length coding. While these are powerful techniques for combating bit errors when they occur at bit error rates (BER) less than 10xe2x88x923, typical wireless channels can have much higher bit error rates. Channel coding can be used to further protect the bitstream in such harsh channel conditions but lowers the data throughput. Thus problems of efficient channel coding exist for MPEG4 and related compression methods in high error rate channels.
Hagenauer, Rate-Compatible Punctured Convolutional Codes (RCPC Codes) and their Applications, 36 IEEE Tr.Comm. 389 (1988), discloses punctured convolutional codes as channel codes with the property that different rate codes are compatilble and can thus easily apply unequal error protection for different parts of an information sequence or block.
The present invention recognizes the advantages of and provides unequal error protection channel coding for compressed video with data partitioning by using higher error protection for packet header information and motion data than for texture data. Further, the header (and bit stuffing) information may have higher error protection than the motion data, so three levels of error protection can exist in each data packet (highest for header and bit stuffing, next highest for motion data, and lowest for texture data). Simillarly, shape data may have a higher error protection than the texture data and at least as high as the motion vector data but less than or equal to header and bit stuffing information.
This has advantages including more efficient channel coding.